JP6394016B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter or the like, or a multifunction machine having a plurality of functions.

Conventionally, a toner image on an image carrier is primarily transferred onto an intermediate transfer belt, which is an endless intermediate transfer member, and then secondary transferred from the intermediate transfer belt to a transfer material such as paper by a secondary transfer unit. An intermediate transfer type image forming apparatus for forming an image is well known. Then, by using an intermediate transfer belt having an elastic layer (hereinafter, also referred to as “elastic intermediate transfer belt”) as an intermediate transfer belt, a concave portion of a paper having unevenness (for example, Rezac 66 (registered trademark name)) is formed. In addition, a technique capable of transferring toner is known (for example, see Patent Document 1).
In addition, in order to prevent image defects such as abnormal transfer and to ensure separation of the transfer material from the intermediate transfer belt and the secondary transfer belt, an intermediate transfer belt having a high volume resistivity is used. A technique for offsetting the next transfer roller upstream is known. An example of such a technique is Patent Document 2.

  The aforementioned uneven paper generally has a certain thickness because it gives unevenness to the paper. However, for image forming apparatuses having an elastic intermediate transfer belt, thin paper is used as part of a wide range of paper types. Response is also required. In order to ensure sheet separation in response to such demands, by using a secondary transfer belt unit system having a secondary transfer belt instead of a secondary transfer roller or charger, uneven paper transfer and thin paper separation are achieved. There is also known a technique for achieving both of these (for example, a combination of Patent Documents 1 and 2).

  However, in the conventional configuration using both the elastic intermediate transfer belt and the secondary transfer belt unit, an abnormal image is generated due to discharge before the secondary transfer portion (secondary transfer nip) (hereinafter also referred to as “pre-nip discharge”). There was a problem that occurred. In particular, an image forming apparatus having a conventional configuration in which an intermediate transfer belt having no elastic layer is used and the secondary transfer roller of the secondary transfer belt unit is offset upstream is provided with an elastic layer as described later. An intermediate belt with no margin has more margin for pre-nip discharge. Further, when a secondary transfer roller is used, there is a problem that thin paper cannot be separated.

  The present invention has been made in view of the above-described circumstances, and image formation capable of simultaneously solving thin paper separation and prevention of abnormal images due to discharge before the secondary transfer portion while ensuring uneven paper transferability. An object is to provide an apparatus.

In order to achieve the above object, the present invention provides an image carrier on which a toner image is repeatedly formed, and a secondary transfer unit that primarily transfers the toner image on the image carrier and performs secondary transfer onto a transfer material. An intermediate transfer belt having an elastic layer, a secondary transfer belt that sucks and conveys a transfer material after secondary transfer, a first rotating member that supports the intermediate transfer belt, and the secondary transfer unit. A second rotating member that is capable of contacting the first rotating member via the intermediate transfer belt and the secondary transfer belt and that supports the secondary transfer belt. An image forming apparatus that applies a secondary transfer bias in a state where a transfer material is sandwiched between the secondary transfer belt and the intermediate transfer belt, and transfers a toner image on the intermediate transfer belt to the transfer material, The secondary transfer bias is constant applied and AC applied. In applied bias for superimposing bets, the secondary transfer bias is applied to said first rotary member, said second rotary member is grounded, the traveling path of the intermediate transfer belt of the secondary transfer portion upstream through the secondary transfer belt along the second rotating member, said first travel path of the secondary transfer belt via the intermediate transfer belt downstream of the secondary transfer portion A pre- nip which is disposed along the member and has a length of a portion where the intermediate transfer belt is wound around the second rotating member when a constant current of the secondary transfer bias is −60 μA to −120 μA. The image forming apparatus has an amount of 4 mm or more.

  According to the present invention, the above configuration simultaneously solves transfer material separability (particularly thin paper) and prevention of abnormal images due to discharge before the secondary transfer portion while ensuring transferability of uneven paper as a transfer material. Therefore, a wide variety of transfer materials can be handled.

1 is a schematic overall configuration diagram of a printer according to an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic enlarged configuration diagram illustrating a main configuration around an image forming unit in FIG. 1. 1 is a schematic configuration diagram of a transfer unit employed in a printer according to Embodiment 1 of the present invention. 6 is a table showing experimental results on the presence or absence of pre-nip discharge when the offset amount (pre-nip amount) of the secondary transfer roller relative to the repulsive roller is changed for two types of intermediate transfer belts that differ only in material and specifications. It is a figure explaining the definition of pre-nip amount, Comprising: It is explanatory drawing which shows the positional relationship of a repulsion roller, a secondary transfer roller, the intermediate transfer belt which has an elastic layer, and a pre-transfer roller. (A) is a case where the offset of the secondary transfer roller relative to the repulsive roller is small in the conventional example (shown without offset in the figure), and (b) is a case where the offset is sufficiently secured in this embodiment. It is a figure explaining the generation | occurrence | production state of prenip discharge, respectively. FIG. 10 is a simplified block diagram illustrating a control configuration of a main part and a transfer unit according to Modification 1; 10 is a chart showing a transfer current correction data table that is changed according to an image area ratio in Modification 1. FIG. 10 is a simplified block diagram illustrating a control configuration of a main part and a transfer unit according to a second modification. 10 is a chart showing a transfer current correction data table that is changed according to absolute humidity in Modification 2. FIG. 10 is a simplified block diagram illustrating a control configuration of a main part and a transfer unit according to a third modification. 10 is a flowchart showing a main operation sequence of Modification 3. It is a chart which shows the determination table for every absolute humidity. FIG. 14 is a table relating to the correction data table of the transfer current changed according to the flowchart of FIG. 12 and the resistance classification of FIG.

  Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In each embodiment and the like, components (members and components) having the same function and shape are described once unless they are confused, and the description thereof is omitted by giving the same reference numerals. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, the reference numerals are shown in parentheses to distinguish them from those of the embodiments.

First, as an example of an image forming apparatus to which the present invention is applied, a printer that is a so-called tandem intermediate transfer type image forming apparatus will be described. First, a basic overall configuration of the printer will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic overall configuration diagram of a printer according to an image forming apparatus to which the present invention is applied, and FIG. 2 is a schematic enlarged configuration diagram showing a main configuration around the image forming unit in FIG.
As shown in FIG. 1, the printer 100 includes an image forming unit 102 disposed above the apparatus main body 101, a transfer unit 7 serving as a transfer unit disposed below the image forming unit 102, and a lower part of the transfer unit 7. , A fixing unit 104 disposed on the left side of the transfer unit 7, and a paper discharge unit 105 disposed on the left side of the fixing unit 104.

As shown in FIGS. 1 and 2, the image forming unit 102 includes four process units 6Y, 6Y for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). 6M, 6C, 6K. The four process units 6Y, 6M, 6C, and 6K have drum-shaped photoreceptors 1Y, 1M, 1C, and 1K corresponding to the color toner images to be formed. Around the photoreceptors 1Y, 1M, 1C, 1K, charging devices 2Y, 2M, 2C, 2K, developing devices 5Y, 5M, 5C, 5K, drum cleaning devices 4Y, corresponding to the color toner images to be formed. 4M, 4C, 4K, a static eliminator (not shown), and the like. The process units 6Y, 6M, 6C, and 6K use Y, M, C, and K toners of different colors, but have the same configuration. Above the process units 6Y, 6M, 6C and 6K, an optical writing unit 3 for irradiating the surface of the photoreceptors 1Y, 1M, 1C and 1K with laser light L to write an electrostatic latent image is arranged. It is provided (means that it is provided by being arranged, or provided at a determined position).
The process unit 6Y includes a photosensitive cartridge 1Y, a charging device 2Y, a developing device 5Y, and a drum cleaning device 4Y integrally in a cartridge housing frame (not shown), and constitutes a process cartridge that is detachably installed on the apparatus main body 101. ing. The other process units 6M, 6C, and 6K also constitute process cartridges in the same manner as described above. As a result, the operability of replacement of the above-described components, developer, etc. constituting the process units 6Y, 6M, 6C, 6K is improved.

  Below the process units 6Y, 6M, 6C, and 6K, a transfer unit 7 is disposed as a belt device including an endless intermediate transfer belt 8 that is a belt member. In addition to the intermediate transfer belt 8, the transfer unit 7 includes a plurality of stretching rollers disposed inside the loop, a secondary transfer roller 18 disposed outside the loop, a tension roller 16, a belt cleaning device 20, A lubricant application device 35 and the like are included. Here, the intermediate transfer belt 8, the secondary transfer roller 18, the secondary transfer bias power source (not shown), the tension roller 16, the belt cleaning device 20, and the lubricant application device 35 constitute an intermediate transfer unit 19.

  The intermediate transfer belt 8 is arranged in a loop shape with a substantially inverted triangular posture. Inside the loop of the intermediate transfer belt 8, four primary transfer rollers 9Y, 9M, 9C, and 9K, a driven roller 10, a drive roller 11, a secondary transfer counter roller 12, three cleaning counter rollers 13, 14, 15 and an application brush opposing roller 17 are disposed. Each of these rollers functions as a stretching roller that hangs the intermediate transfer belt 8 around a part of its peripheral surface and performs belt stretching (meaning that the belt is stretched under tension). The cleaning counter rollers 13, 14, and 15 do not necessarily have to have a function of applying a constant tension, and may be driven to rotate as the intermediate transfer belt 8 rotates. The intermediate transfer belt 8 is endlessly moved and traveled in the clockwise direction in the drawing by the rotation of the driving roller 11 that is driven to rotate clockwise in the drawing by a driving means such as a driving motor (not shown).

  The four primary transfer rollers 9Y, 9M, 9C, and 9K disposed inside the belt loop sandwich the intermediate transfer belt 8 between the photoreceptors 1Y, 1M, 1C, and 1K. As a result, the primary surface for Y, M, C, and K in which the front surface of the intermediate transfer belt 8 and the photoreceptors 1Y, 1M, 1C, and 1K come into contact (meaning that they come into contact with each other). A transfer nip is formed. The primary transfer rollers 9Y, 9M, 9C, and 9K are each applied with a primary transfer bias having a polarity opposite to that of toner transferred by a power source (not shown).

  An optical sensor 31, also called a toner adhesion amount sensor, is disposed above the intermediate transfer belt 8 that is wound around the outer peripheral surface of the drive roller 11. The optical sensor 31 is a reflective optical sensor, and has a light emitting element and a light receiving element, and has a function as a toner density detecting means and a toner image position detecting means. The light emitted from the light emitting element of the optical sensor 31 is reflected by a toner patch (not shown) which is a test pattern created on the intermediate transfer belt 8, and is received by the light receiving element and converted into a signal. By reading the change in the signal, the information on the test pattern is analogized to detect the amount of toner patch adhesion, which is used to adjust and control the developing bias and the charging bias.

Further, the intermediate transfer belt 8 is sandwiched between the secondary transfer counter roller 12 disposed inside the belt loop and the secondary transfer roller 18 disposed outside the belt loop. As a result, a secondary transfer nip as a secondary transfer portion where the front surface of the intermediate transfer belt 8 and the secondary transfer roller 18 abut (hereinafter referred to as “secondary transfer nip portion as a portion including the secondary transfer nip”). Is also formed). A secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 18 by a power source (not shown).
The paper transfer belt is bridged by the secondary transfer roller, several support rollers, and a drive roller, and the intermediate transfer belt 8 and the paper transfer belt are placed between the secondary transfer roller 18 and the secondary transfer counter roller 12. It is good also as a structure inserted | pinched.

  The belt cleaning device 20 removes toner, paper dust, and the like on the intermediate transfer belt 8 and cleans them. As shown in FIG. 2, the three cleaning facing rollers 13, 14, 15 disposed on the inner side of the belt loop are the three cleaning brush rollers 21, 24, 27 of the belt cleaning device 20 disposed on the outer side of the belt loop. The intermediate transfer belt 8 is sandwiched between the two. As a result, a cleaning nip is formed in which the front surface of the intermediate transfer belt 8 and the cleaning brush rollers 21, 24, 27 come into contact with each other. Each cleaning brush roller 21, 24, 27 functions as a brush-like rotating body that contacts the front surface of the intermediate transfer belt 8 to remove and hold the toner on the intermediate transfer belt 8.

Further, the belt cleaning device 20 has a toner recovery roller 22 as a toner recovery rotating body that corresponds to and contacts the cleaning brush rollers 21, 24, 27 and recovers the toner held by the cleaning brush rollers 21, 24, 27. , 25, 28 are arranged. Further, the belt cleaning device 20 corresponds to and contacts the toner recovery rollers 22, 25, and 28, and the toner recovery blades 23 and 26 as recovery blade members that scrape off the toner attached to the toner recovery rollers 22, 25, and 28. , 29 are arranged. Further, the belt cleaning device 20 is provided with conveying screws 30a and 30b as toner conveying rotary members for collecting and conveying the toner scraped off by the toner collecting blades 23, 26 and 29.
The belt cleaning device 20 can be integrally replaced with the intermediate transfer belt 8. When the lifetime setting is different between the belt cleaning device 20 and the intermediate transfer belt 8, the belt cleaning device 20 may be detachable from the printer main body independently of the intermediate transfer belt 8.

  A lubricant application device for protecting the surface of the intermediate transfer belt 8 by applying a lubricant to the surface of the intermediate transfer belt 8 on the downstream side in the moving direction of the intermediate transfer belt 8 adjacent to the belt cleaning device 20. 35 is disposed. The lubricant application device 35 is in contact with a solid lubricant 37 such as a zinc stearate block (block) and the solid lubricant 37, and lubricant powder obtained by scraping the solid lubricant 37 by rotation is transferred to the intermediate transfer belt 8. And an application brush roller 36 as an application member to be applied to the surface. Although the lubricant application device 35 is provided in this embodiment, it may not be necessary depending on the toner to be used, the material of the intermediate transfer belt, and the surface friction coefficient thereof, and the application is not necessarily required.

  A recording paper P including a sheet as a sheet as a transfer material is adsorbed to the sheet conveyance path between the secondary transfer nip N that is a secondary transfer unit and the fixing unit 104, and downstream in the sheet conveyance direction. A belt conveyance unit 32 for conveyance is disposed. The belt conveyance unit 32 is provided in order to reliably feed a sheet (particularly, a thin paper with poor separation property) to the fixing unit 104 while supplementing the sheet separation property at the secondary transfer nip portion N.

As shown in FIG. 1, the paper feed unit 103 is provided for each of the upper and lower paper feed cassettes 41 and 42 that store the recording paper P, and the paper feed cassettes 41 and 42. Are provided with paper feeding rollers 41 and 42 for feeding the uppermost recording paper P one by one.
Near the front side of the secondary transfer nip on the downstream side of the paper feed path 43 connected to the paper feed unit 103, the recording paper P sent from the paper feed unit 103 is received and directed toward the secondary transfer nip. A registration roller pair 46 is disposed to be sent out at the timing.

  The fixing unit 104 as a fixing device receives the recording paper P sent out from the secondary transfer nip, and performs fixing processing by applying heat and pressure to the unfixed toner image on the recording paper P. The secondary transfer nip is arranged on the left side of the figure.

The paper discharge unit 105 includes a paper discharge roller pair 48 that discharges the recording paper P that has been fixed out of the printer main body 101, a paper discharge tray 49 on which the discharged recording paper P is placed, and a recording paper that has been fixed. A sheet conveyance path switching member or the like is provided for reversing the P side and feeding it again to the secondary transfer nip. In addition, a switchback conveyance path that reverses the recording paper P, a sheet conveyance path switching member, a double-side conveyance path, and the like are provided so that images can be formed on both the front and back sides of the recording paper P.
The printer 100 also includes a toner replenishing device that detachably accommodates Y, M, C, and K toner bottles that replenish Y, M, C, and K toners to the developing devices 5Y, 5M, 5C, and 5K. 47 is also provided. As shown in FIG. 1, the printer 100 also includes a control unit 38 that controls the operation of each unit / apparatus described above, and a temperature / humidity detection sensor that is an environmental condition detection unit (not shown).

  Next, the operation of the printer 100 will be described. The operation of the printer 100 is performed under the command of the control unit 38. When full-color image information (image data) is sent from a personal computer (not shown) or the like, the drive roller 11 is driven to rotate, and the intermediate transfer belt 8 is moved and traveled. The stretching rollers other than the driving roller 11 are rotated following the movement / running of the intermediate transfer belt 8. At the same time, the photoreceptors 1Y, 1M, 1C, and 1K of the process units 6Y, 6M, 6C, and 6K are rotationally driven by a motor (not shown) while the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K are charged by the charging devices 2Y, 2M, and 2C. , 2K are uniformly charged. Then, the charged surfaces of the photoreceptors 1Y, 1M, 1C, and 1K are irradiated and scanned from the optical writing unit 3 that is modulated in accordance with image data and signals for forming an electrostatic latent image. An electrostatic latent image is formed by the laser beam L. The electrostatic latent images formed on the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K are developed with the color toners of the developing devices 5Y, 5M, 5C, and 5K, so that the photoreceptors 1Y, 1M, 1C, and Y, M, C, and K toner images are formed on 1K. The Y, M, C, and K toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 8 in the above-described primary transfer nips for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 8.

  On the other hand, in the paper feed unit 103, one of the paper feed cassettes 41 or 42 is selected by a user operation of an operation / display unit (not shown), and the recording paper P is loaded by driving the paper feed roller 44 or 45 on the selected side. Each sheet is fed out and conveyed to the registration roller pair 46. The leading edge of the fed recording paper P is temporarily stopped at the nip portion of the registration roller pair 46 to correct an oblique shift and the like, and thereafter, can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 8. The registration roller pair 46 is driven. By driving the registration roller pair 46, the recording paper P is sent to the secondary transfer nip portion N formed between the secondary transfer counter roller 12 and the secondary transfer roller 18, and is on the intermediate transfer belt 8. The four-color superimposed toner image is secondarily transferred onto the recording paper P at once. Thereby, a full-color image is formed on the surface of the recording paper P. The recording paper P after the formation of the full-color image is conveyed from the secondary transfer nip to the fixing unit 104 where the unfixed toner image is melted and fixed on the recording paper P by applying heat and pressure. The recording sheet P after the fixing process is discharged and stacked on the discharge tray 49 by the discharge roller pair 48 as an output image.

The photoreceptors 1Y, 1M, 1C, and 1K after the Y, M, C, and K toner images are primarily transferred to the intermediate transfer belt 8 are cleaned of the transfer residual toner and the like by the drum cleaning devices 4Y, 4M, 4C, and 4K. Processing is performed. Thereafter, after being neutralized by a neutralizing lamp (not shown), it is again uniformly charged by the charging devices 2Y, 2M, 2C, and 2K to prepare for the next image formation. Further, the intermediate transfer belt 8 after the primary transfer onto the recording paper P is subjected to cleaning processing such as residual toner by the belt cleaning device 20.
In the operation of the printer 100 described above, the full-color image forming operation has been described. However, it is of course possible to form a single-color toner image or two or more colors of superimposed toner images. That is, as the image forming mode transmitted from the personal computer (not shown), there are a single color image mode or monochrome image mode for forming a single color toner image, and a color image mode for forming a superposed toner image of two or more colors. . In accordance with each of these modes, any one of the four primary transfer rollers 9Y, 9M, 9C, and 9K, or any two or more of them are moved up and displaced in the primary transfer unit, thereby corresponding photosensitive resin. A toner image is formed by bringing the intermediate transfer belt 8 into contact with the bodies 1Y, 1M, 1C, and 1K.

  In recent years, in addition to plain paper that has been widely used as recording paper, special recording paper that is used for thermal transfer such as special paper having an uneven surface or iron print as a design has been increasingly used. When such special paper is used, transfer defects are more likely to occur when the toner image on the intermediate transfer belt 8 on which the color toners are superimposed is secondarily transferred onto the paper, as compared with conventional plain paper. Therefore, in this printer 100, an elastic layer having a low hardness is provided on the intermediate transfer belt 8, and a toner layer or a recording paper with poor smoothness is provided at the secondary transfer nip N (hereinafter also simply referred to as “transfer nip N”). It can be deformed. By providing the intermediate transfer belt 8 with an elastic layer having a low hardness so that the intermediate transfer belt 8 has elasticity, the surface of the intermediate transfer belt 8 can be elastically deformed following local irregularities. As a result, good adhesion can be obtained without excessively increasing the transfer pressure with respect to the toner layer, there is no loss of character transfer, and the paper having poor smoothness, for example, the above-described Rezak 66 (registered trademark). Name) and the like, and a transfer image having excellent uniformity and no transfer unevenness can be obtained. The transfer material includes an OHP film sheet to which a toner image can be transferred in addition to the recording paper and paper described above.

  The intermediate transfer belt 8 used in the printer 100 includes at least a base layer, an elastic layer, and a surface coat layer.

  Examples of the material used for the elastic layer of the intermediate transfer belt 8 include elastic members such as elastic material rubber and elastomer. Specifically, butyl rubber, fluorine rubber, acrylic rubber, EPDM, NBR, acrylonitrile-butadiene-styrene rubber, natural rubber, isoprene rubber, styrene-butadiene rubber, butadiene rubber, urethane rubber, syndiotactic 1,2-polybutadiene , Epichlorohydrin rubber, polysulfide rubber, polynorbornene rubber, thermoplastic elastomer (eg polystyrene, polyolefin, polyvinyl chloride, polyurethane, polyamide, polyurea, polyester, fluororesin) One type or two or more types selected from the group can be used. However, it is not limited to the said material.

The thickness of the elastic layer depends on the hardness and the layer structure, but is preferably in the range of 0.07 to 0.8 [mm]. More preferably, the range of 0.25-0.5 [mm] is good.
Here, if the thickness of the elastic layer is less than 0.07 [mm], the pressure on the toner on the intermediate transfer belt 8 at the secondary transfer nip portion N becomes high, so that a transfer dropout is likely to occur. Further, it is not preferable because the transfer rate of the toner is lowered. On the other hand, when the thickness of the elastic layer exceeds 0.8 [mm], it is preferable from the viewpoint of dot reproducibility (the dot shape collapses due to expansion and contraction of the elastic layer. This is worse as the elastic layer is thicker). Absent.

  The hardness of the elastic layer is preferably 10 ° ≦ HS ≦ 65 ° (JIS-A). Although the optimum hardness varies depending on the layer thickness of the intermediate transfer belt 8, if the hardness is less than 10 ° (JIS-A), a transfer dropout is likely to occur. On the other hand, when the elastic layer has a hardness exceeding 65 ° (JIS-A), it is difficult to stretch the above-mentioned rollers, and because it is stretched by long-term stretching, it is not durable and requires early replacement. It is not preferable from the point which becomes.

  The base layer of the intermediate transfer belt 8 is made of a resin with little elongation. Specifically, materials used for the base layer include polycarbonate, fluororesin (ETFE, PVDF, etc.), polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, Styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer) Styrene-octyl acrylate copolymer and styrene-phenyl acrylate copolymer), styrene-methacrylic acid ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene) -Phenyl methacrylate copolymer, etc.), steel -Α-chloromethyl acrylate copolymer, styrene resin such as styrene-acrylonitrile-acrylate ester copolymer (monopolymer or copolymer containing styrene or styrene substitution product), methyl methacrylate resin, methacryl Acid butyl resin, ethyl acrylate resin, butyl acrylate resin, modified acrylic resin (silicone modified acrylic resin, vinyl chloride resin modified acrylic resin, acrylic / urethane resin, etc.), vinyl chloride resin, styrene-vinyl acetate copolymer, chloride Pinyl-vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, polyester polyurethane resin, polyethylene, polypropylene, polybutadiene, polyvinylidene chloride, ionomer resin, polyurethane resin, silicone Fat, ketone resins, ethylene - can be used ethyl acrylate copolymer, xylene resin and polyvinyl butyral resin, polyamide resin, one kind or two kinds or more selected from the group consisting of modified polyphenylene oxide resin. However, it is not limited to the said material.

  In addition, in order to prevent the elastic layer made of a rubber material having a large elongation from extending, a core layer made of a material such as a canvas may be provided between the base layer and the elastic layer. Examples of materials for preventing elongation used in the core layer include natural fibers such as cotton and silk, polyester fibers, nylon fibers, acrylic fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinyl chloride fibers, and polyvinylidene chloride fibers. , One or more selected from the group consisting of synthetic fibers such as polyurethane fiber, polyacetal fiber, polyfluoroethylene fiber and phenol fiber, inorganic fibers such as carbon fiber and glass fiber, and metal fibers such as iron fiber and copper fiber Threaded or woven fabric can be used. Of course, the material is not limited to the above. The above-described yarn may be twisted in any manner, such as one or a plurality of filaments twisted, one-twisted yarn, various twisted yarns, double yarn, or the like. Further, for example, fibers of a material selected from the above material group may be blended. Of course, the yarn can be used after being subjected to an appropriate conductive treatment. On the other hand, the woven fabric can be any woven fabric such as knitted weave, and of course, a woven fabric that has been woven can also be used and can be subjected to a conductive treatment.

  The coat layer on the surface of the intermediate transfer belt 8 is for coating the surface of the elastic layer and is composed of a layer having good smoothness. The material used for the coating layer is not particularly limited, but generally, a material that reduces the adhesive force of the toner to the surface of the intermediate transfer belt 8 and improves the secondary transfer property is used. For example, one or more types of polyurethane, polyester, epoxy resin, etc., or materials that reduce surface energy and increase lubricity, such as fluorine fats, fluorine compounds, fluorocarbons, titanium oxide, silicon carbide, etc. Can be used by dispersing one type or two or more types or changing the particle size as required. Further, it is also possible to use a material such as a fluorine-based rubber material in which a heat treatment is performed to form a fluorine layer on the surface and the surface energy is reduced.

  If necessary, the base layer, the elastic layer, or the coating layer is, for example, carbon black, graphite, metal powder such as aluminum or nickel, tin oxide, titanium oxide, antimony oxide, indium oxide, for the purpose of adjusting resistance. Conductive metal oxides such as potassium titanate, antimony oxide-tin oxide composite oxide (ATO), and indium oxide-tin oxide composite oxide (ITO) can be used. Here, the conductive metal oxide may be coated with insulating fine particles such as barium sulfate, magnesium silicate, and calcium carbonate. However, it is not limited to the said material.

  In the printer 100 to which the present invention is applied, the intermediate transfer belt 8 having the elastic layer having the above-described configuration as the intermediate transfer belt 8 (hereinafter, also simply referred to as “intermediate transfer belt 8”) in order to ensure transferability of the uneven paper. Is used. The toner of each color formed on each of the photoreceptors 1Y, 1M, 1C, and 1K is batch-transferred to the recording paper P at the secondary transfer nip portion N after the primary transfer process superimposed on the intermediate transfer belt 8. Next transfer process is performed. This elastic intermediate transfer belt has, for example, a base layer of about 50 to 100 [μm] of polyimide or polyamideimide on the inner layer, and an elastic layer using acrylic rubber or the like is laminated thereon. It has been configured. The elastic intermediate transfer belt is further coated with a coating for imparting releasability to the surface layer. The elastic layer is generally about 100 [μm] to 1 [mm].

According to the rubber property and elasticity of the elastic intermediate transfer belt, the toner can be transferred to the concave portion of the paper having irregularities by applying a transfer pressure necessary for the secondary transfer. When the elastic intermediate transfer belt is used as described above, it is necessary to apply a sufficient transfer pressure to the elastic layer, so that a somewhat high transfer pressure is required for the secondary transfer. Therefore, for example, a configuration in which a plurality of pressure mechanisms are prepared as the secondary transfer pressure and the transfer pressure is changed according to the paper may be used. In the secondary transfer nip portion N which is the secondary transfer portion, the necessary transfer pressure to be applied is usually about 40 to 300 [N] in total pressure.
However, in any case, by applying a transfer pressure necessary for transfer, the recording paper P is made to have high adhesion to the intermediate transfer belt 8 so that the secondary transfer nip portion N is formed. Even if the recording paper P comes out, the recording paper P may not be separated from the intermediate transfer belt 8 and may cause a separation failure. This is remarkable in a system using the above-described secondary transfer roller 18 which is a roller-like rotating member.
Therefore, in the first embodiment to which the present invention described below is applied, as an example, a secondary transfer belt unit 49 that is a secondary transfer belt system is used as shown in FIG.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic configuration diagram of a transfer unit 7A employed in the printer according to Embodiment 1 of the present invention.
The first embodiment is mainly different from the printer 100 shown in FIG. 1 in that a transfer unit 7A as a transfer unit is used instead of the transfer unit 7. The configuration of the first embodiment other than this difference is the same as that of the printer 100 shown in FIG. Hereinafter, the configuration and operation of Embodiment 1 will be described in detail focusing on the above differences. The transfer unit 7A of the first embodiment is different from the transfer unit 7 of FIGS. 1 and 2 in that an intermediate transfer unit 19A is used instead of the intermediate transfer unit 19, and a secondary transfer roller 18 is used instead of the secondary transfer roller 18. The difference is that a secondary transfer belt unit 49 having a transfer roller 51 and the like is used.

Compared with the intermediate transfer unit 19, the intermediate transfer unit 19A uses a repulsive roller 12A that is a secondary transfer counter roller, and a pre-transfer roller 34 is newly provided near the upstream side of the repulsive roller 12A. The difference is that the traveling track is changed. The repulsive roller 12A is a so-called backup roller that functions as a first rotating member that supports the intermediate transfer belt 8, and is made of a metal core 12Aa and an elastic formed of rubber or the like on the outer periphery of the core 12Aa. Layer 12Ab. The cored bar 12Aa of the repulsive roller 12A is connected to a secondary transfer bias power source 33 and a ground (GND) as a secondary transfer bias applying means for applying a secondary transfer bias (voltage) so that the current is constant. Has been.
Here, the intermediate transfer belt 8, the repulsive roller 12A, the tension roller 16 (see FIG. 2), the belt cleaning device 20 (see FIG. 2), the pre-transfer roller 34, the power source 33, and the lubricant application device 35 (see FIG. 2) The intermediate transfer unit 19A is configured.

The pre-transfer roller 34 is rotatably supported by the apparatus main body 101 via a shaft in the vicinity of the upstream side of the repulsive roller 12A inside the belt loop. The pre-transfer roller 34 is provided in order to hold the traveling track of the intermediate transfer belt 8 at an appropriate position when the secondary transfer roller 51 is offset with respect to the repulsive roller 12A as will be described later.
As described above, the intermediate transfer belt 8 is a secondary transfer portion serving as a secondary transfer portion that primarily transfers the toner images on the photoreceptors 1Y, 1M, 1C, and 1K and performs secondary transfer onto the recording paper P as a transfer material. The elastic layer described above is conveyed to the transfer nip portion N.

The secondary transfer belt unit 49 includes a secondary transfer belt 50, a secondary transfer roller 51, a separation roller 52, a cleaning counter roller 53 that also serves as a tension roller, a cleaning blade 54, an optical sensor counter roller 55, and an optical sensor 31. Yes. The secondary transfer belt 50 is stretched around a secondary transfer roller 51, a separation roller 52, a cleaning facing roller 53, and an optical sensor facing roller 55. The secondary transfer belt unit 49 spans the secondary transfer belt 50 so that the secondary transfer belt 50 can travel to the secondary transfer roller 51, the separation roller 52, the cleaning counter roller 53, and the optical sensor counter roller 55 via the four axes of the above rollers. It has a substantially trapezoidal shape when viewed from the front.
Of the components constituting the secondary transfer belt unit 49, the secondary transfer belt 50, the secondary transfer roller 51, and the separation roller 52 are generally necessary components. The roller 55 may be provided as necessary.

  As the secondary transfer belt 50, polyimide resin (PI) is used in the embodiment, and the thickness is 80 μm. In addition to the polyimide resin (PI), various materials such as polyamide imide resin (PAI) and polyvinylidene fluoride resin (PVDF) can be used as the secondary transfer belt 50. The secondary transfer belt 50 may be a belt having an elastic layer in addition to the above materials.

The secondary transfer roller 51 includes a metal core part 51a and a rubber elastic layer 51b formed on the outer periphery of the core part 51a. A cored bar 51a of the secondary transfer roller 51 is connected to ground (GND).
The optical sensor 31 is arranged by changing from the position on the intermediate transfer belt 8 shown in FIG. 2 to the position shown in FIG. In the present embodiment, the optical sensor 31 is used for image density adjustment. That is, the present embodiment has an adjustment mode for adjusting the image forming conditions, and when adjusting the image forming conditions, a test patch is created by changing the developing bias and the charging bias. Then, the test patch is transferred onto the secondary transfer belt 50, and the adjustment is performed by detecting the toner density of the test patch with the optical sensor 31.

  As shown in FIG. 3, the secondary transfer entrance guide upper 48 a functions as a guide member, and travels along the travel path (movement locus) of the upstream intermediate transfer belt 8 between the repulsive roller 12 </ b> A and the secondary transfer roller 51. It is arranged along. Further, a secondary transfer inlet guide lower portion 48b serving as a guide member is provided while maintaining a predetermined gap from the secondary transfer inlet guide upper portion 48a. The recording sheet P fed from the registration roller pair 46 shown in FIG. 2 is guided to the secondary transfer nip portion N by the secondary transfer entrance guide upper 48a and the secondary transfer entrance guide lower 48b. On the other hand, in the vicinity of the downstream side of the secondary transfer belt 50 wound around the separation roller 52 of the secondary transfer belt unit 49, as a guide member for guiding the recording paper P separated and conveyed by the action of the separation roller 52. The secondary transfer outlet guide 56 is provided.

3, the intermediate transfer belt 8 is moved and running in the direction of the arrow (clockwise direction), the toner image on the intermediate transfer belt 8 and the recording sheet P, the secondary transfer belt through the secondary transfer roller 51 The secondary transfer is performed while being sandwiched by 50. At this time, a secondary transfer bias having the same polarity as the toner on the intermediate transfer belt 8 (which may include a superimposed AC, pulse, etc.) is applied to the core bar 12Aa of the repulsive roller 12A by the power source 33. A transfer current flows. Due to this transfer current, the superimposed toner images on the intermediate transfer belt 8 are collectively put on the recording paper P by the action of an electric field between the intermediate transfer belt 8 and the secondary transfer belt 50 and the secondary transfer roller 51. Secondarily transferred. The transfer current flowing through the cored bar 12Aa of the repulsive roller 12A flows through the intermediate transfer belt 8 and the secondary transfer belt 50 into the elastic layer 51b of the secondary transfer roller 51, and further from the cored bar 51a to ground (GND). It flows to.

  In the secondary transfer belt unit 49, when the recording paper P passes through the secondary transfer nip portion N, an attractive force acts on the secondary transfer belt 50, which is stronger than the attractive force on the intermediate transfer belt 8. For this reason, the recording paper P can be reliably separated from the intermediate transfer belt 8. For this reason, by adopting the “elastic intermediate transfer belt + secondary transfer belt method”, in this embodiment, it is possible to cope with a wide variety of transfer materials (paper type / sheet type) from thin paper to thick paper uneven paper. Yes.

  However, in such a configuration, it was confirmed through experiments that discharge at the secondary transfer nip N entrance is likely to occur. FIG. 4 shows the presence or absence of pre-nip discharge when the offset amount (pre-nip amount described later) of the secondary transfer roller 51 with respect to the repulsive roller 12A is changed with respect to two types of intermediate transfer belts 8 having different materials and specifications. It is a chart showing an experimental result. This experiment was performed in a test machine corresponding to the printer 100 of FIG. 1 by replacing the transfer unit 7 shown in FIG. 2 with the transfer unit 7A of the first embodiment shown in FIG. Note that the contact distance between the recording paper P and the intermediate transfer belt 8 formed by the offset in front of the secondary transfer nip N is referred to as a pre-nip amount. The pre-nip can be formed by offsetting the secondary transfer roller 51 with respect to the repulsive roller 12A. Therefore, when a roller position other than the position of the secondary transfer roller 51 is fixed, the offset amount and the pre-nip amount are one-to-one. Correspond. Here, if the trajectory of the intermediate transfer belt 8 before the secondary transfer nip portion N, the diameter and hardness of the pre-transfer roller 34, and the like are changed, the pre-nip amount also changes.

In FIG. 4, two types of intermediate transfer belts 8 having different materials and specifications include an elastic intermediate transfer belt (described as an elastic belt in FIG. 4) used in the first embodiment and a polyimide resin (PI). ), And the total thickness and length of both are the same. The pre-nip amount is changed by offsetting only the secondary transfer roller 51 to the upstream side of the travel path of the intermediate transfer belt 8, and the discharge margin in the combination of each experimental item is the secondary transfer current for the plain paper and the thin paper. It is the result confirmed by changing [−μA] to 6 levels. As plain paper,
“Type-6000,70W” manufactured by Ricoh Co., Ltd. was used, and “NBS Ricoh copy printing paper 45k paper” was used as the thin paper.
As an evaluation of the experimental results in FIG. 4, ◯ indicates that no abnormal discharge image is generated, Δ indicates that a slight occurrence occurs, and × indicates that a discharge abnormality is easily found. The higher the current, the higher the voltage, which is severe with respect to discharge. Therefore, there is a margin so that discharge does not occur in a wider current range (at high current).

In the present embodiment, −120 [μA] is used as the set current from the viewpoint of transferability, and it is essential that no discharge occurs at least in this setting. From this point of view, the elastic belt (the intermediate transfer belt 8 used in Embodiment 1) requires a pre-nip amount of 4 mm or more, and the PI belt requires 2 mm or more.
Note that the experimental results (numerical values) in FIG. 4 are merely examples of the configuration of the present embodiment, and are generally due to various factors such as the thickness of the intermediate transfer belt, each roller diameter, hardness, and process linear velocity. Since the discharge margin varies, the required pre-nip amount differs for each image forming apparatus. However, if the configuration is the same, it can be said that the elastic intermediate transfer belt has a smaller margin to discharge than the PI belt.

  Although the description is mixed, here, the definition of the pre-nip amount will be described with reference to FIG. FIG. 5 is a diagram for explaining the definition of the pre-nip amount, and is an explanatory diagram showing the positional relationship between the repulsive roller 12A, the secondary transfer roller 51, the intermediate transfer belt 8 having an elastic layer, and the pre-transfer roller 34. In FIG. 5, a straight line L1 indicated by a broken line connecting the axial center 12o of the repulsive roller 12A and the axial center 51o of the secondary transfer roller 51, and a broken line descending from the axial center 51o of the secondary transfer roller 51 to the intermediate transfer belt 8. An angle α [deg] formed with the perpendicular line L2 shown in FIG. At this time, the pre-nip amount is defined as 2π × (radius of the secondary transfer roller 51) × α / 360 °. That is, the length of the portion of the intermediate transfer belt 8 that is wound around the secondary transfer roller 51 is defined as the pre-nip amount. For this reason, the pre-nip amount varies depending on the diameter of the secondary transfer roller 51 and the locus of the intermediate transfer belt 8 as described above, but is determined by the offset amount of the secondary transfer roller 51 when these are fixed. The relationship between the pre-nip amount and discharge in FIG. 4 is obtained by changing the pre-nip amount by changing the offset amount in this way.

In other words, the offset of the secondary transfer roller 51 can be expressed as follows. That is, the travel path of the intermediate transfer belt 8 is along the secondary transfer roller 51 via the secondary transfer belt 50 on the upstream side of the secondary transfer nip N, and the travel path of the secondary transfer belt 50 is the secondary transfer nip. via the intermediate transfer belt 8 that is disposed along the repulsive roller 12A at a downstream side of the N.

There are various abnormal images in the pre-nip discharge. However, for example, thin paper is generally weak against discharge, and, for example, white streaks appear on the entire paper. Thick paper including uneven paper has a margin for discharge compared to thin paper, but the front and rear edges of the paper are characterized by being easy to discharge due to poor adhesion to the intermediate transfer belt.
For this reason, the "elastic intermediate transfer belt + secondary transfer belt system" can provide a wide range of paper type (paper type) compatibility from the viewpoint of transferability and paper separation, but an abnormal image due to discharge occurs. There was a problem that it was easy. Therefore, in this embodiment, in the “elastic intermediate transfer belt + secondary transfer belt method”, the secondary transfer roller 51 is offset to the upstream side in the transfer material conveyance direction X, so that a pre-nip more sufficient than the conventional one is formed and abnormal. The greatest feature is in preventing discharge. The transfer material conveyance direction X is a sheet conveyance direction as well as a sheet conveyance direction.

  With reference to FIG. 3, this embodiment will be described in more detail. FIG. 3 shows the transfer unit 7A of the first embodiment and is also a detailed view of the secondary transfer nip portion. In this embodiment, the outer diameters of the repulsive roller 12A and the secondary transfer roller 51 are the same, the secondary transfer roller 51 has a Shore A hardness of 70 degrees, and the repulsive roller 12A has an Asker C of 50 degrees. When Asker C 50 ° repulsive roller 12A was measured on Shore A, it was 25 degrees. The secondary transfer roller 51 having a Shore A hardness of 70 degrees was measured by Asker C and found to be 85 degrees. This is because the harder secondary transfer roller 51 is more likely to utilize the rubber property of the intermediate transfer belt 8 having an elastic layer, but the combination of hardness and the magnitude relationship are not limited to the above-described numerical values and relationships, and various You may use things. In addition, the relationship between the outer diameters of the repulsive roller 12A and the secondary transfer roller 51 is a different numerical value, or the combination of both large and small can provide the effects of the present invention.

In the present embodiment, as shown in FIG. 3, the secondary transfer roller 51 is offset upstream in the transfer material conveyance direction X. As a result, the recording paper P is transported in close contact with the intermediate transfer belt 8 on the front side of the secondary transfer nip portion N, so that a gap between the intermediate transfer belt 8 and the recording paper P in front of the secondary transfer nip portion N is formed. Elimination prevents discharge. Further, the effect of the present invention will be explained from the electric field distribution. As the transfer electric field distribution, the strongest electric field acts in the secondary transfer nip portion N, and gradually weakens from this point toward the upstream side in the transfer material conveyance direction X. It has become. When the recording paper P comes into contact with the intermediate transfer belt 8 where the electric field distribution is strong, discharge occurs in the process (discharge occurs in the gap). Therefore, discharge can be prevented by bringing the intermediate transfer belt 8 and the recording paper P into contact with the front side (right side in FIG. 3) of the secondary transfer nip N where the electric field is weak.
In this embodiment, as described above, constant current control is used as bias control for secondary transfer. This is because a constant transfer voltage (= transfer electric field) can be obtained for the secondary transfer nip portion N regardless of the resistance of the repulsive roller 12A as a transfer member and the recording paper P as a transfer material. is there.

With reference to FIG. 6, the effect of the said embodiment of this invention is supplemented. FIG. 6A is an explanatory diagram for explaining the state of occurrence of pre-nip discharge when the offset of the secondary transfer roller 51X with respect to the repulsive roller 12X is small in the conventional example (shown without offset in the figure). FIG. 6B is a diagram for explaining the state of occurrence of pre-nip discharge when the offset is sufficiently secured in the present embodiment example.
When the recording paper P enters the secondary transfer nip N, a discharge is generated in the gap between the surface of the intermediate transfer belt 8 of the repulsive rollers 12X and 12A to which the secondary transfer bias is applied and the recording paper P (upper surface in the figure). The occurrence of this is called pre-nip discharge. For example, as shown in FIG. 6A, when the secondary transfer roller 51X is not offset with respect to the transfer material conveyance direction X, an entrance gap is formed between the repulsive roller 12X and the recording paper P. Pre-nip discharge occurs. The reason why the roller is referred to as a repulsive roller is that a roller to which a secondary transfer bias is applied transfers with a repulsive force that applies a negative bias to negatively charged toner.

On the other hand, as shown in FIG. 6B, by offsetting the secondary transfer roller 51 with respect to the repulsive roller 12A, the recording paper P comes into close contact with the intermediate transfer belt 8 before the secondary transfer nip portion N. When the repulsive roller 12A, which has a high electric field, reaches the gap, the gap is small and pre-nip discharge can be prevented.
The pre-nip discharge is performed by the voltage of the secondary transfer rollers 51 and 51X, the intermediate transfer belt 8, the repulsive rollers 12X and 12A, and the secondary transfer belt 50 (omitted in FIGS. 6A and 6B). The ease of occurrence varies depending on the resistance, material, type of recording paper P, conveyance state, and the like. It has been found from the experiment described with reference to FIG. 4 that the pre-nip discharge is particularly likely to occur when the intermediate transfer belt 8 is an elastic belt. Therefore, discharge cannot be prevented with the conventional offset amount, but discharge can be prevented by increasing the offset amount more than the conventional one as in this embodiment.

  Here, I supplement the contents described in the background art. Patent Document 1 discloses a method of adjusting the secondary transfer linear velocity with a configuration in which the secondary transfer roller is offset upstream by an elastic belt and a secondary transfer roller for the purpose of ensuring dot reproducibility. Yes. However, when an elastic belt is used as the intermediate transfer belt, the problem of achieving both “thin paper separation” and “prevention of abnormal discharge images” cannot be solved. For this reason, it is impossible to expect the effects of the present embodiment described above.

Further, in Patent Document 2, image defects such as abnormal transfer are prevented and the transfer material can be reliably separated from the intermediate transfer belt, the secondary transfer belt, or the secondary transfer roller with a simple configuration. For the purpose, the following configuration is disclosed. That is, the secondary transfer roller (which is a roller forming a secondary transfer nip in the secondary transfer belt) is offset upstream with respect to the intermediate transfer belt and the secondary transfer belt having a volume resistance of 10 ⁸ Ωcm or more. The structure to perform is disclosed.
However, when an elastic belt is used as the intermediate transfer belt, the problem that an abnormal discharge occurs with an offset configuration similar to that of the intermediate transfer belt having no elastic layer cannot be solved. For this reason, it is impossible to expect the effects of the present embodiment described above.

(Modification 1)
With reference to FIG.7 and FIG.8, the modification 1 of Embodiment 1 is demonstrated. FIG. 7 is a simplified block diagram showing a control configuration of a main part and a transfer unit of the first modification, and FIG. 8 is a table relating to a transfer current correction data table which is changed according to the image area ratio.
In the first modification, the secondary transfer bias control is characterized in order to further increase the discharge margin based on the first embodiment. As in the configuration of the first embodiment, the secondary transfer roller 51 is offset to the upstream side in the transfer material conveyance direction X by the “elastic intermediate transfer belt + secondary transfer belt method”. As described above, the use of this configuration improves the margin with respect to the pre-nip discharge. Naturally, the pre-nip discharge tends to become an abnormal image as the secondary transfer bias increases. Even if the toner is discharged, if the toner has a large amount of charge, the toner will carry the charge, or even if it is discharged, it will be sufficiently attracted to the intermediate transfer belt and will not become an abnormal image. Alternatively, if the total amount of toner such as two-color superposition is large, there is still a margin for discharge. For example, if the resistance of the toner is high, the margin for discharge is improved. Conversely, if the toner has a low resistance or such a conductive agent is used, an abnormal image is likely to occur. For example, carbon black is often used as a colorant for black toner. However, since carbon black has conductivity, the resistance tends to decrease, and even if the resistance does not decrease, other colors of the discharge can be used. It may be weaker than toner.
Therefore, in the first modification, in order to further improve the discharge margin from the first embodiment, the secondary transfer bias is controlled according to the image area ratio of the secondary transfer nip portion N, which is the secondary transfer portion, as a control of the secondary transfer bias. The margin is further improved by controlling the next transfer bias.

  As shown in FIG. 7, the printer 100 according to the first modification includes a control unit 38 as a control unit that controls the entire printer 100. The control unit 38 includes a CPU 38a having functions of a calculation unit and a control unit, and an information storage unit. The information storage unit includes a RAM including a nonvolatile RAM that stores data, a ROM, a HDD (Hard Disk Drive), and the like. In the present embodiment, it is composed of various control programs required for various processes, a PDL (Page Description Language) processing system of a printer, a ROM 38b storing system initial setting values, a RAM 38c for work memory, and the like. .

The CPU 38a drives the above-described units and device units of the printer 100 via the information storage unit based on various signals from various sensors provided in the printer 100 and signals set by various keys of the operation display unit 58. The control of the part etc. is performed. As various sensors, the optical sensor 31 is mentioned as a typical one.
A main drive unit of the above-described units and device units in Modification 1 includes a secondary transfer bias power source 33 (including a power circuit and the like) of the transfer unit 7A shown in FIG. Although not shown in FIG. 7, as described in FIG. 1, actuators such as motors and solenoids disposed in the image forming unit 102, the paper feeding unit 103, the fixing unit 104, and the paper discharging unit 105 are provided. Can be mentioned.

  Information on various sensors and information / data from the optical sensor 31 are periodically or temporarily stored in a RAM 38c including a nonvolatile RAM. The ROM 38b stores in advance a control program for exerting the function of the CPU 38a, necessary related data, and the like. Necessary relational data include a calculation formula for calculating the image area ratio, fixed data such as a target secondary transfer bias current value, a data table of image area ratio and transfer current shown in FIG.

The control unit 38 controls driving of each unit / device unit based on a control program stored in the ROM 38b. The CPU 38a uses the image area ratio corresponding to the toner image on the intermediate transfer belt 8 transferred to the recording paper P at the secondary transfer nip N to form an electrostatic latent image on the photoreceptors 1Y, 1M, 1C, 1K. Therefore, it functions as an image area ratio calculating means for calculating based on the writing image data signal. Further, the control unit 38 (the CPU 38a) controls the secondary transfer bias power supply 33 via a power supply circuit (not shown) so as to change the target secondary transfer bias current in accordance with the calculated image area ratio. It functions as a first control means.
The toner image on the intermediate transfer belt 8 transferred to the recording paper P at the secondary transfer nip portion N includes a single color or a superposed toner image of two or more colors.

In FIG. 7, the image data signal transmitted from the personal computer 40 to the control unit 38 via the image processing unit 39 includes information such as the recording paper size and the number of prints in addition to the image data to be written. . The image processing unit 39 performs various image processing based on the image data signal and transmits an image data signal to be written to the control unit 38. The control unit 38 transmits the received image data signal to be written to the optical writing unit 3.
The operation display unit 58 includes keys and switches for instructing the printer 100 to perform various operations, and display / notification means such as a liquid crystal display device. The operation display unit 58 and the control unit 38 transmit and receive an image forming condition signal and a command signal for driving and controlling the liquid crystal display device.
The image processing unit 39 may be incorporated in the configuration of the control unit 38 and may be a CPU for image processing. The image data signal transmitted to the control unit 38 is not limited to the one described above, and is read by this image reading apparatus by installing an image reading apparatus such as a scanner in the printer 100 separately from the personal computer 40. It may be image data of a document image.

FIG. 8 is a correction data table for the above-described control and the transfer current to be passed through the secondary transfer portion as the secondary transfer bias corresponding to the image area ratio. In the first modification, the image area ratio, which is the ratio of the image area at the secondary transfer portion, is calculated, and the secondary transfer current value is corrected via the secondary transfer bias power source 33 accordingly. The secondary transfer current is constant current control, and the target current is set by a PWM (pulse width modulation) signal transmitted from the above-described image processing CPU 38a or the control unit (not shown) of the image forming unit 102. It is controlled. By changing the PWM signal according to the image area ratio, the target transfer current is changed in real time from time to time while performing constant current control.
Specifically, the CPU 38a of the control unit 38 calculates the image area ratio at intervals of 50 mm for each sub-scanning direction (rotational direction of the intermediate transfer belt 8), and the calculation result corresponds to FIG. Control is performed based on the table. As the interval in the sub-scanning direction (belt rotation direction) is narrower, a higher effect can be obtained. However, as in Modification 1, 50 mm is sufficiently effective, and even if the interval is wider, there are some effects.

FIG. 8 will be further described with a specific example. The image area ratio is defined with respect to the writable width. For example, the case where one color is printed over the entire writable width is 100%. For example, 50% is printed every other dot. If multiple colors overlap, simply add the proportions of each color. Therefore, it is 200% for all solids of two colors.
When the control is performed based on FIG. 8, for example, when a monochrome solid image is printed, an output equivalent to 100% is performed. This 100% means that the reference transfer current, which is the target transfer current, is output as it is. For example, in this case, it is −120 μA. When the image area ratio is 5%, it is 40% from the chart, and −120 μA × 40% = − 48 μA.

  According to the modified example 1, by performing the above-described control, it is possible to further improve the discharge margin as compared with the first embodiment while ensuring transferability. The relationship with the image area ratio in FIG. 8 is preferably made in accordance with the characteristics of each image forming apparatus, and it goes without saying that it is not limited to this chart. Furthermore, the control may be changed according to the color of the toner as well as a simple image area. For example, if the black toner does not require much current, it is possible to obtain a further effect by correcting the calculation of the image area ratio so that it is equivalent to 90% in all solids.

(Modification 2)
With reference to FIG.9 and FIG.10, the modification 2 of the modification 1 is demonstrated. FIG. 9 is a simplified block diagram showing a control configuration of a main part and a transfer unit according to the second modification, and FIG. 10 is a table relating to a correction data table of a transfer current changed according to absolute humidity.
In the second modification, the discharge margin is further improved by correcting the transfer current based on the detection result of the temperature and humidity in the printer 100 based on the first modification. The control configuration of the second modification is mainly different from that of the first modification in that a temperature / humidity sensor 59 is newly provided as shown in FIG. 9 and a control unit 38A is used instead of the control unit 38. . The configuration of Modification 2 other than this difference is the same as that of Modification 1.

The temperature / humidity sensor 59 functions as temperature / humidity detection means (or environmental condition detection means) for detecting temperature / humidity (or environmental conditions) in the printer 100.
In addition to the function of the control unit 38 in the first modification, the control unit 38A in the second modification changes the target secondary transfer bias current according to the temperature and humidity detected by the temperature and humidity sensor 59. It also has a function as a means. The ROM 38b of the control unit 38A stores in advance a control program for causing the function of the CPU 38a, necessary relation data, and the like. Necessary relational data include a calculation formula for calculating the image area ratio and absolute humidity, fixed data such as a target secondary transfer bias current value, and the absolute humidity shown in FIG. For example, a data table with a transfer current.

  The control unit 38A controls driving of each unit / device unit based on a control program stored in the ROM 38b. The CPU 38a of the control unit 38A controls the power supply 33 for the secondary transfer bias via a power supply circuit (not shown) so as to change the target secondary transfer bias current according to the temperature and humidity detected by the temperature and humidity sensor 59. It functions as a second control means.

  FIG. 10 is a correction data table for the above-described control and the transfer current to be passed through the secondary transfer portion as the secondary transfer bias corresponding to the absolute humidity. In the second modification, the temperature and humidity (relative humidity: RH) are detected by the temperature / humidity sensor 59, and then the absolute humidity is calculated based on the following equation 1 (Tetens equation).

Then, by applying a correction factor for each absolute humidity, the discharge margin is improved by setting the secondary transfer bias to a value according to the environment. For example, when an environment such as 10 ° C. and 15% RH is considered, the resistance member constituting the secondary transfer portion is cold and the resistance generally increases. Therefore, when the same transfer current control as in other environments is performed, the transfer voltage becomes very high and discharge becomes easy.
On the other hand, since a very high current is not required for transferability, lowering the target transfer current from the viewpoint of transferability and discharge prevention (further, since the attraction force to the intermediate transfer belt is also smaller, the separation property is improved). preferable.
Therefore, in FIG. 10, the absolute humidity 1.41 at 10 ° C. and 15% RH is 80% as a correction factor (the calculation of this absolute humidity is based on the above-described formula 1). If a 40% image is printed in this environment, the target secondary transfer current is -120 μA × 70% (correction based on the image area ratio) × 80% (environment) along with the previous image area correction. Correction under conditions) = − 67.2 μA.

  In the second modification, the correction as shown in FIG. 10 is performed. However, it is preferable that the correction data table is made according to the characteristics of the image forming apparatus, and the correction rate for each absolute humidity is not limited to this. Incidentally, in FIG. 10, even when the absolute humidity is as high as 18 or more, the output of the transfer current is corrected to 90%, but this is not due to discharge but from transferability. As described above, the effects of the present invention (corresponding to a wide variety of transfer materials (paper types)) can be further obtained by making corrections not only from discharge but also from the viewpoint of transferability.

The second modification is based on the first modification, but is not limited thereto, and may be configured based only on the first embodiment. Configuration in this case is ing to that removed the configuration associated with the image area ratio of the first modification.

(Modification 3)
With reference to FIGS. 11-14, the modification 3 of the modification 2 is demonstrated. FIG. 11 is a simplified block diagram showing a control configuration of a main part and a transfer unit of the third modification, and FIG. 12 is a flowchart showing an operation sequence when performing detection of the combined resistance of the secondary transfer part. FIG. 13 is a chart showing a determination table for each absolute humidity.
In the third modification, the combined resistance of the secondary transfer portion is further detected based on the second modification, and the transfer current is corrected according to the detection result, thereby further improving the discharge margin.
The control configuration of the modification 3 is different from that of the modification 2 in that a voltmeter 60 for detecting the combined resistance of the secondary transfer unit is newly provided as shown in FIG. The main difference is that the control unit 38B is used. The configuration of Modification 3 other than this difference is the same as that of Modification 2.

The voltmeter 60 functions as a substitute for the combined resistance detecting means for detecting the combined resistance of the intermediate transfer belt 8, the repulsive roller 12 </ b> A, the secondary transfer belt 50, and the secondary transfer roller 51 in the secondary transfer portion. To do.
The control unit 38B is for the secondary transfer bias so as to change the target secondary transfer bias current according to the combined resistance (the voltage that is a substitute value) detected by the voltmeter 60 as a substitute for the combined resistance detecting means. It functions as a third control means for controlling the power source 33. The ROM 38b of the control unit 38B stores in advance a control program (flowchart in FIG. 12) for causing the function of the CPU 38a of the control unit 38B, necessary relation data, and the like. Necessary relational data include calculation formulas for calculating the image area ratio and absolute humidity, fixed data such as a target secondary transfer bias current value, and the data table of FIG. 8, as well as FIG. 10, FIG. 13 and FIG. 14 or the like.
The voltmeter 60, which is a specific configuration of the combined resistance detecting means, is normally included in the secondary transfer bias power supply 33 and its power supply circuit.

  With reference to FIG. 12, the operation flow of the combined resistance detection of the secondary transfer unit will be described. First, the rotation operation of the printer 100 as the image forming apparatus is started. In this case, at least the intermediate transfer unit 19A and the secondary transfer belt unit 49 only need to rotate (step S1). Next, the power supply 33 is activated, and after the rotational operation of the intermediate transfer unit 19A and the secondary transfer belt unit 49 is stabilized, the intermediate transfer belt 8, repulsive roller 12A, and secondary transfer belt 50 constituting the secondary transfer unit. A test current is passed through the secondary transfer roller 51 (step S2). This test current is preset and is a current for detecting the combined resistance of the intermediate transfer belt 8, the repulsive roller 12A, the secondary transfer belt 50, and the secondary transfer roller 51, and has an adverse effect on the members. Any number is acceptable as long as it is not. Further, the current for detecting the combined resistance may be changed each time depending on the environment and other factors so that the detection is easy. In the third modification, a setting value of −120 μA is commonly used in all environments.

After applying the test current and waiting for the current to stabilize for about 200 msec, the voltage of the secondary transfer portion is measured and sampled by the voltmeter 60 for about 200 msec. The sampling period of voltage measurement is 20 msec, and 21 samples are acquired. The 21 samples are averaged, and the average value of the voltages is used as a detection result as a substitute value of the combined resistance in the secondary transfer portion (step S3).
Next, the CPU 38a of the control unit 38B automatically performs data processing for the detection result, which is divided into the sections 1 to 5 according to the chart (data table) shown in FIG. 13 (step S4). FIG. 13 is a determination table for each absolute humidity. This is because the resistance of each of the members constituting the secondary transfer portion varies depending on the environmental conditions, and therefore the conditions are changed depending on which environment is detected.
The series of combined resistance detection and determination operation for each absolute humidity described above are performed during the preparation operation when the power is turned on or when the transfer unit 7A is rotated at the start of image formation, thereby shortening the operation time. Is also possible.

  FIG. 14 is a table relating to the correction data table of the transfer current changed according to the flowchart of FIG. 12 and the resistance classification of FIG. In FIG. 13, for example, when the category 4 is selected in the resistance detection operation, the correction rate of 90% of the category 4 is applied to the target current. Therefore, for example, when an image with an image area ratio of 5% is printed under an environmental condition of 10 ° C. and 15% RH, the image area ratio correction, the environmental condition correction, and the combined resistance correction are performed with respect to a reference current that is a target transfer current. The product of the two is the final output. That is, the final output is -120 μA × 40% (image area ratio correction) × 80% (environmental condition correction) × 90% (composite resistance correction) ≈34.6 μA.

  As described above, according to the third modification, the effect of the present invention (wide variety) can be achieved by further improving the discharge margin by applying correction to the image area ratio, the environmental condition, and the combined resistance. An image forming apparatus having a transfer material (paper type) capability) can be provided.

The third modification is based on the second modification, but is not limited thereto, and may be configured based only on the first embodiment. Configuration in this case is ing to that removed the configuration associated with the image area ratio of the first modification. In addition, but it may also only the first modification to a configuration in which the base.
As shown in FIG. 3, the image forming apparatus according to the present embodiment includes an intermediate transfer belt 8 having an elastic layer, a secondary transfer belt 50, a repulsive roller 12A that supports the intermediate transfer belt 8, and a secondary transfer belt 50. A toner image on the intermediate transfer belt 8 is transferred to a sheet by a transfer bias at a secondary transfer nip portion N between the repulsive roller 12A and the secondary transfer roller 51. . The intermediate transfer belt 8 is in a sheet conveyance direction which is also a transfer material conveyance direction X rather than a straight line L1 (indicated by a one-dot chain line: see also FIG. 5) connecting the axis center of the repulsive roller 12A and the axis center of the secondary transfer roller 51. It is arranged so as to wind around the secondary transfer roller 51 via the secondary transfer belt 50 on the upstream side. Further, the secondary transfer belt 50 is arranged to wrap around the repulsive roller 12A via the intermediate transfer belt 8 on the downstream side of the straight line L1 in the sheet conveying direction. Thereby, it is possible to solve the separability of the paper and the prevention of the abnormal image due to the discharge before the transfer while ensuring the transferability of the uneven paper or the like.

  The preferred embodiments and the like of the present invention have been described above, but the present invention is not limited to the specific embodiments, and the present invention described in the claims is not limited to the above description. Various modifications and changes are possible within the scope of the gist of the invention. For example, the present invention is not limited to the above-described embodiment and modification examples 1 to 3, but may be a combination of these as appropriate.

  For example, the image forming apparatus to which the present invention is applied is not limited to the type of image forming apparatus described above, and may be another type of image forming apparatus. In other words, the image forming apparatus to which the present invention is applied may be an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or a multifunction machine having a plurality of functions.

  For example, the secondary transfer belt unit 49 is not limited thereto, and the entire secondary transfer belt unit 49 is moved along the travel path of the intermediate transfer belt 8 or transferred between the repulsive roller 12A and the pre-transfer roller 34. You may comprise so that a displacement along the material conveyance direction X is possible. Thereby, the offset amount of the secondary transfer roller 51 with respect to the repulsive roller 12A can be arbitrarily changed.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1Y, 1M, 1C, 1K photoconductor (an example of an image carrier)
2Y, 2M, 2C, 2K Charging device (charging means)
3 Optical writing unit (exposure means)
4,4M, 4C, 4K Drum cleaning device (cleaning means)
5Y, 5M, 5C, 5K Development device (developing means)
6Y, 6M, 6C, 6K Process unit (process cartridge)
7A Transfer unit 8 Intermediate transfer belt 12A Repulsive roller (an example of a first rotating member and a first roller)
19A Intermediate transfer unit 33 Power supply for secondary transfer bias (an example of secondary transfer bias applying means)
38 control unit (example of first control means)
38A control unit (an example of second control means)
38B control unit (an example of third control means)
49 Secondary transfer belt unit 50 Secondary transfer belt 51 Secondary transfer roller (second rotation member, one example of second roller)
59 Temperature / humidity sensor (temperature / humidity detection means, example of environmental condition detection means)
60 Voltmeter (an example of combined resistance detection means)
100 printer (an example of an image forming apparatus)
N Secondary transfer nip (an example of a secondary transfer)
P Recording paper (example of transfer material, paper, sheet-like recording medium)
X Transfer material conveyance direction

JP 2012-208491 A Japanese Patent No. 3554225

Claims (9)

An image carrier on which toner images are repeatedly formed;
An intermediate transfer belt having an elastic layer, wherein the toner image on the image carrier is primarily transferred and conveyed to a secondary transfer portion for secondary transfer to a transfer material;
A secondary transfer belt that sucks and conveys the transfer material after the secondary transfer;
A first rotating member that supports the intermediate transfer belt;
A second rotating member capable of contacting the first rotating member via the intermediate transfer belt and the secondary transfer belt at the secondary transfer unit, and supporting the secondary transfer belt;
An image for transferring a toner image on the intermediate transfer belt to the transfer material by applying a secondary transfer bias while the transfer material is sandwiched between the secondary transfer belt and the intermediate transfer belt at the secondary transfer portion. A forming device,
The secondary transfer bias is an applied bias that superimposes constant application and AC application, the secondary transfer bias is applied to the first rotating member, and the second rotating member is grounded.
The travel path of the intermediate transfer belt through the secondary transfer belt upstream of the secondary transfer part along the second rotary member, the secondary transfer downstream travel path of the secondary transfer portion of the belt Arranged along the first rotating member via the intermediate transfer belt on the side,
An image forming apparatus , wherein when the constant current of the secondary transfer bias is from −60 μA to −120 μA, a pre- nip amount that is a length of a portion where the intermediate transfer belt is wound around the second rotating member is 4 mm or more. The image forming apparatus according to claim 1.
2. The image forming apparatus according to claim 1, wherein the hardness of the second rotating member is higher than that of the first rotating member. The image forming apparatus according to claim 1 or 2,
Secondary transfer bias applying means for applying the secondary transfer bias;
An image area ratio that calculates an image area ratio corresponding to the toner image on the intermediate transfer belt transferred to the transfer material in the secondary transfer portion based on image data for forming a latent image on the image carrier. A calculation means;
First control means for controlling the secondary transfer bias applying means so as to change a target secondary transfer bias current according to the image area ratio calculated by the image area ratio calculating means;
An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 3,
Secondary transfer bias applying means for applying the secondary transfer bias;
Temperature and humidity detection means for detecting temperature and humidity in the image forming apparatus;
Second control means for controlling the secondary transfer bias application means so as to change a target secondary transfer bias current according to the temperature and humidity detected by the temperature and humidity detection means;
An image forming apparatus comprising: The image forming apparatus according to any one of claims 1 to 4,
Secondary transfer bias applying means for applying the secondary transfer bias;
In the secondary transfer portion, and the intermediate transfer belt, the first rotary member, the combined resistance detecting means for detecting the combined resistance of the combined electric resistance of the secondary transfer belt and the second rotary member,
Third control means for controlling the secondary transfer bias applying means so as to change a target secondary transfer bias current according to the combined resistance detected by the combined resistance detecting means;
An image forming apparatus comprising: An intermediate transfer belt having an elastic layer;
A secondary transfer belt;
A first roller that supports the intermediate transfer belt;
A second roller for supporting the secondary transfer belt,
An image forming apparatus for transferring a toner image on the intermediate transfer belt to a sheet by a transfer bias at a transfer nip between the first roller and the second roller;
The transfer bias is an applied bias that superimposes a constant application and an AC application, the transfer bias is applied to the first roller, and the second roller is grounded,
The intermediate transfer belt is wound around the second roller via the secondary transfer belt on the upstream side in the sheet conveyance direction with respect to the straight line connecting the axis center of the first roller and the axis center of the second roller,
The secondary transfer belt is wound around the first roller via the intermediate transfer belt on the downstream side of the straight line with respect to the sheet conveyance direction,
An image forming apparatus in which when the constant current of the transfer bias is from −60 μA to −120 μA, a pre- nip amount, which is a length of a portion where the intermediate transfer belt is wound around the second roller, is 4 mm or more. The image forming apparatus according to claim 6.
The image forming apparatus, wherein the elastic layer of the intermediate transfer belt is laminated on a base layer. The image forming apparatus according to claim 7.
The image forming apparatus, wherein the intermediate transfer belt has a coat layer coated on the elastic layer. The image forming apparatus according to any one of claims 6 to 8,
The image forming apparatus, wherein the hardness of the second roller is higher than the hardness of the first roller.

Images